Lagynochthonius polydentatus is a species of pseudoscorpion in the Chthoniidae family. It is endemic to Australia. It was described in 2008 by Australian arachnologists Karen Edward and Mark Harvey.
The species occurs in the Murchison bioregion of Western Australia. The type locality is a borehole on Sturt Meadows Station, some 40 km north-west of Leonora.
The arachnids are cave-dwelling, terrestrial predators.